Gangland slayings in the Palestinian territories this week have pitted the Islamist gunmen of Hamas against the secular forces of Fatah. The killings defy civilised norms: in December even children were targeted for murder. But the killings also defy political common sense. Ariel Sharon's wall cuts terrorists off from Israeli targets and what happens? The violence - previously justified with the cause of a Palestinian homeland - continues as if nothing had changed, merely finding its outlet in a new set of targets. This makes it appear that Palestinian violence has never really been about a "cause" at all. The violence is, in a strange way, about itself.
Gunnar Heinsohn, a social scientist and genocide researcher at the University of Bremen, has an explanation for why this might be so. Since its publication in 2003, his eccentric and eye-opening Sons and World Power* (not available in English) has become something of a cult book. In Mr Heinsohn's view, when 15 to 29-year-olds make up more than 30 per cent of the population, violence tends to happen; when large percentages are under 15, violence is often imminent. The "causes" in the name of which that violence is committed can be immaterial. There are 67 countries in the world with such "youth bulges" now and 60 of them are undergoing some kind of civil war or mass killing.